Method for fabricating polysilicon liquid crystal display device

ABSTRACT

A method for fabricating a polysilicon liquid crystal display device includes: forming a first amorphous silicon layer on a substrate; forming a photoresist pattern on the first amorphous silicon layer; forming a second amorphous silicon layer over the photoresist pattern and the first amorphous silicon layer; defining a channel region on the first amorphous silicon layer; crystallizing the first and second silicon layers; forming an active layer by patterning the crystallized silicon layers; forming a first insulating layer on the active layer; forming a gate electrode on the first insulating layer; forming source and drain electrodes electrically connected to the active layer; and forming a pixel electrode electrically connected to the drain electrode.

The present invention claims the benefit of Korean Patent ApplicationNo. 2003-99326 filed in Korea on Dec. 29, 2003, which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device, andmore particularly, to a method for fabricating a polysilicon liquidcrystal display device. Although the present invention is suitable for awide scope of applications, it is particularly suited for reducing thenumber of processes fabricating a liquid crystal display (LCD) device.

2. Description of the Related Art

As interest in image display devices and demand for portable informationdevice increase, a thin film type Flat Panel Display (FPD) devices havebeen developed that are replacing traditional Cathode Ray Tubes (CRT)type display devices. In particular, a liquid crystal display (LCD)device having the characteristic of optical anisotropy has replaced theCRT. Further, the liquid crystal display device has been used innotebook computers, desktop monitors, or the like because it has anexcellent resolution, color rendering capability and picture quality.

A liquid crystal display device includes a color filter substrate, anarray substrate and a liquid crystal material formed between the twosubstrates. A thin film transistor, which uses amorphous silicon orpolycrystalline silicon as a channel layer, is used as a switchingdevice of the liquid crystal display device. A process for fabricatingthe liquid crystal display device usually requires a plurality ofphoto-mask processes in fabricating the array substrate including thethin film transistor.

FIG. 1 is a plan view showing a unit pixel of an array substrate of aliquid crystal display device of the related art. In a typical liquidcrystal display device, the ‘N’ number of gate lines and the ‘M’ numberof data lines cross each other, forming the ‘N×M’ number of pixels. Forthe purpose of simplicity, only one pixel is presented in the FIG. 1. Asshown in FIG. 1, the array substrate 10 includes: a pixel electrode 18formed on a pixel region; gate lines 16 and data lines 17 disposedvertically and horizontally on the substrate 10; and a thin filmtransistor used as a switching device, which is formed at a regionadjacent to where the gates lines 16 and the data lines 17 cross eachother.

The thin film transistor includes: a gate electrode 21 connected to thegate line 16; a source electrode 22 connected to the data line 17; and adrain electrode 23 connected to the pixel electrode 18. Also, the thinfilm transistor includes: a first insulating layer (not shown) and asecond insulating layer (not shown) for insulating the gate electrode 21and source/drain electrodes 22 and 23; and an active layer 24 forforming a conductive channel between the source electrode 22 and thedrain electrode 23 by a gate voltage supplied to the gate electrode 21.The source electrode 22 is electrically connected to a source region ofthe active layer 24 and the drain electrode 23 is electrically connectedto a drain region of the active layer 24 through first contact holes 40a formed in the first and second insulating layers. Since a thirdinsulating layer (not shown) has a second contact hole 40 b exposing thedrain electrode 23, the drain electrode 23 and the pixel electrode 18are electrically connected to each other through the second contact hole40 b.

FIGS. 2A to 2G are views showing fabrication processes along the lineI-I of the liquid crystal display device shown in FIG. 1 showingfabrication processes according to the related art. As shown in FIG. 2A,the active layer 24 of polysilcon is formed on a transparent substrate10, such as a glass, by using photolithography.

Next, as shown in FIG. 2B, a first insulating layer 15 a is formed overthe active layer 24, and a conductive layer 30 is formed on the firstinsulating layer to form a gate electrode.

Next, as shown in FIG. 2C, a gate electrode 21 is formed on the activelayer 24 with the first insulating layer 15 a interposed therebetween bypatterning the conductive layer 30 using a photolithography process.Thereafter, source/drain regions are formed by injecting N+ or P+ typehigh density impurity ions into side regions of the active layer 24using the gate electrode 21 as a mask. The source/drain regions areformed for ohmic contacts to the source/drain electrodes.

Next, as shown in FIG. 2D, after a second insulating layer 15 b as aninterlayer insulating layer is deposited over the entire surface of thesubstrate 10 on which the gate electrode 21 is formed, the first contactholes 40 a for electrical connection between the source/drain regionsand the source/drain electrodes are formed by removing parts of thefirst insulating layer 15 a and the second insulating layer 15 b throughphotolithography.

Thereafter, as shown in FIG. 2E, after a conductive material isdeposited over the entire surface of the substrate 10, the sourceelectrode 22 connected to the source region 24S and the drain electrode23 connected to the drain region 24 d are formed through the firstcontact holes 40 a. At this time, a part of the conductive materialconstructing the source electrode 22 is extended to form the data line.

Next, as shown in FIG. 2F, after the third insulating layer 15 c, anorganic insulating layer, such as Acryl, is deposited over an entiresurface of the substrate 10, a second contact hole 40 b is formed toexpose the drain electrode 23 by photolithography.

Finally, after transparent conductive materials, such as Indium TinOxide (ITO), are deposited over the entire surface of the substrate 10on which the third insulating layer 15 c is formed. The pixel electrode18 is connected to the drain electrode 23 through the second contacthole 40 b an patterned by photolithography.

A process for injecting impurity ions into the active layer to formsource and drain regions and a process for activating the impurity ionsare required in the related art processes for fabricating the TFT. Inorder to perform these processes, special equipment is required, whichleads to increase fabrication costs in fabricating a thin filmtransistor. In addition, photolithography processes include a pluralityof sub-processes such as photoresist coating, exposure, development andetching etc. As a result, a plurality of photolithography processeslowers production yield and are prone to cause defects in the thin filmtransistor. Further, since a mask used in the photolithography is veryexpensive, if many masks are used for the processes, fabrication costsfor the liquid crystal display device are also raised.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method forfabricating a polysilicon liquid crystal display device thatsubstantially obviates one or more of the problems due to limitationsand disadvantages of the related art.

An object of the present invention is to fabricate a liquid crystaldisplay device with a smaller number of masks for fabricating apolysilicon liquid crystal display device without a separateion-injection process for forming source and drain regions on an activelayer.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described herein,there is provided a method for fabricating a polysilicon liquid crystaldisplay device includes: forming a first amorphous silicon layer on asubstrate; forming a photoresist pattern on the first amorphous siliconlayer; forming a second amorphous silicon layer over the photoresistpattern and the first amorphous silicon layer; defining a channel regionon the first amorphous silicon layer; crystallizing the first and secondsilicon layers; forming an active layer by patterning the crystallizedsilicon layers; forming a first insulating layer on the active layer;forming a gate electrode on the first insulating layer; forming sourceand drain electrodes electrically connected to the active layer; andforming a pixel electrode electrically connected to the drain electrode.

In another aspect, a method of fabricating a polysilicon liquid crystaldisplay device includes: forming a gate electrode on a substrate;forming a first insulating layer on the gate electrode; forming a firstamorphous silicon layer on the first insulating layer; forming aphotoresist pattern on the first amorphous silicon layer; forming asecond amorphous silicon layer over the photoresist pattern and thefirst amorphous silicon layer; defining a channel region on the firstamorphous silicon layer; crystallizing the first and second amorphoussilicon layers; defining an active layer; forming source and drainelectrodes on the crystallized second silicon layers; and forming apixel electrode electrically connected to the drain electrode.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a plan view showing a part of the related art polysiliconliquid crystal display device.

FIGS. 2A to 2G are cross-sectional views along the line I-I of FIG. 1showing fabrication processes according to the related art.

FIGS. 3A to 3F are cross-sectional views showing processes for a methodfor fabricating a polysilicon liquid crystal display device inaccordance with a first embodiment of the present invention.

FIGS. 4A to 4G are cross-sectional views showing processes for a methodof fabricating a polysilicon liquid crystal display device in accordancewith a second embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

A polysilicon liquid crystal display device has rapid operationcharacteristics because of high electron mobility characteristics ofpolysilicon. Since polysilicon is not a complete conductive material,such as metal, and has high ohmic resistance when in contact with metal,a process of improving ohmic characteristics with a metal layer includesinjecting P+ or N+ type high density impurity ions into a polysiliconlayer when a source electrode or a drain electrode is in contact withthe polysilicon layer. However, this process requires a separateion-injection process and an activation process of activating theinjected ions by heat-processing the polysilicon layer to activate andstabilize the crystalline lattice of the polysilicon layer since thepolysilicon layer into which the ions are injected is damaged by theinjected ions.

To get rid of the activation process, a first amorphous silicon layer isformed followed by a photoresist pattern being formed on the amorphoussilicon layer and then a second amorphous silicon layer is formed on thephotoresist pattern. When forming the second amorphous silicon layer,high density impurity ions are injected into the second amorphoussilicon layer while it is being formed so that the second amorphoussilicon layer will include the impurities.

Next, a lift-off process is performed on the first and second amorphoussilicon layers having a photoresist pattern interposed therebetween toremove the photoresist pattern and a portion of the second amorphoussilicon layer formed on the photoresist pattern, so that a channelregion is defined. Then, the first and the second amorphous siliconlayers are crystallized. In the crystallization process, activation ofthe high density impurities included in the second amorphous siliconlayer and crystallization of the first and second silicon layers areperformed at the same time. In embodiments of the present invention, apolysilicon liquid crystal display device is fabricated using theabove-described method.

FIGS. 3A to 3F are cross-sectional views showing processes for a methodfor fabricating a polysilicon liquid crystal display device inaccordance with a first embodiment of the present invention. As shown inFIG. 3A, a buffer layer 302 of silicon oxide (SiO₂) or silicon nitride(SiN_(x)) is formed on a substrate 301 to prevent impurities included inthe substrate 301 from being diffused into a silicon layer that is to becrystallized, and a first amorphous silicon layer 303 is formed on thebuffer layer 302. The first amorphous silicon layer 303 is formed byplasma enhanced chemical vapor deposition (PECVD). After forming thefirst amorphous silicon layer 303, a photoresist film is applied on thefirst amorphous silicon layer 303. A photoresist pattern film 304remains on a channel region after exposure and development.

A second amorphous silicon layer 305 is formed on the photoresist filmpattern 304 and the first amorphous silicon layer 305 by PECVD. Thesecond amorphous silicon layer 305 is deposited in a plasma state whilemixing high density impurities into the second amorphous silicon layer305. When a device to be formed is a P-type TFT, ions of a group IIIelements, such as Boron, can be mixed into the plasma. In the case of aN-type TFT, ions of a group V elements, such as Phosphorous, can bemixed into the plasma.

The second amorphous silicon layer 305 formed by the above methodbecomes an amorphous silicon layer having impurity ions. The secondamorphous silicon layer 305 does not have to be thick and can be formedwith a predetermined thickness capable of improving contactcharacteristics with a metal layer. In this embodiment, the firstamorphous silicon layer 303 can have a thickness of about 500 angstroms(Å) and the second amorphous silicon layer 305 can have a thickness ofabout 200 angstroms (Å).

Next, the photoresist film pattern 304 and a portion of the secondamorphous silicon layer 305 formed on the photoresist film pattern areremoved at the same time by a lift-off process. In the lift-off process,a thin film existing at an upper portion of the photoresist is takenaway in the process of stripping the photoresist pattern 304. Inembodiments of the present invention, a channel region 330 is defined bythe lift-off process. As a result of the lift-off process, only thefirst amorphous silicon layer 303 is left on the channel region 330, anda dual layer of the first and second amorphous silicon layers 303 and305 is left at other regions.

Next, as shown in FIG. 3B, the formed first and second amorphous siliconlayers are crystallized. The crystallization process includes a step ofperforming dehydrogenation by heating the amorphous silicon layers 303and 305 and a step of crystallizing the amorphous silicon layers. Thecrystallization process will now be described in detail.

The hydrogen ions function can cause defects during the process ofcrystallizing amorphous silicon. More particularly, the hydrogen ionsare removed in advance because they are likely to explode, which cancause damage a silicon layer in the crystallization process. In order toget rid of hydrogen included within the formed amorphous silicon layers,the amorphous silicon layers are put into a furnace and heated at about400° C. so as to remove the hydrogen.

After the dehydrogenation process, the process of crystallizing theamorphous silicon layers is performed. An amorphous silicon layer can beheated at a high-temperature furnace. In a laser crystallization method,amorphous silicon layer can be momentarily heated to be crystallized byusing excimer laser energy. In the laser crystallization method, a largegrain size can be formed in the crystallization process so that electronmobility can be significantly improved in comparison to the heatingmethod of crystallization. Accordingly, the laser crystallization methodis effective when forming a TFT requiring rapid operation.

After crystallizing the amorphous silicon layer, as shown in FIG. 3C,the polysilicon layer is patterned into an active layer 303A using asecond mask. The process of patterning the active layer may be performedby using photolithography. More particularly, an exposure process, adevelopment process and a process of etching a polysilicon layer areperformed using the second mask on the photoresist film, which has beenapplied on the polysilicon layer. The polysilicon layer can beeffectively patterned by dry etching.

Impurity ions included within the second amorphous silicon layer 305 areactivated during the process of crystallizing the amorphous siliconlayers 303 and 305. This activation allows the impurity ions disposed ina lattice to rearrange themselves into a stable form while thecrystallization process is performed. Consequently, this process doesnot require injecting of impurity ions or a separate activation processto form the active layer 303 a including source and drain regions 305 aand 305 b.

After forming the active layer 303 a, as shown in FIG. 3C, a firstinsulating layer 307 composed of silicon oxide or silicon nitride isformed over the entire surface of the substrate, including the activelayer 303 a by PECVD. In addition, a conductive layer is formed on thefirst insulating layer 307 by sputtering. The conductive layer is forforming a gate electrode. The conductive layer can be aluminum (Al) ormolybdenum (Mo). Also, a dual layer of aluminum and molybdenum can beused as the conductive layer. After forming the conductive layer, theconductive layer is patterned to form a gate line (not shown) and a gateelectrode 306.

Next, a second insulating layer 308 composed of silicon nitride orsilicon oxide is formed on the gate electrode 306 and the firstinsulating layer 307. The second insulating layer may be formed byPECVD.

After forming the second insulating layer, as shown in FIG. 3D, contactholes are formed within the second insulating layer 306. The contactholes expose a source region 305 a and a drain region 305 b. The contactholes include a first contact hole 309 a and a second contact hole 309b.

Next, as shown in FIG. 3E, a conductive layer is formed on the secondinsulating layer 308 on which the first contact hole 309 a and thesecond contact hole 309 b are formed, and the conductive layer ispatterned to form source and drain electrodes 310 and 311.

Next, a third insulating layer 313 composed of an organic layer or aninorganic layer is formed on the entire surface of the substrate onwhich the source and drain electrodes are formed. Then, a contact holefor exposing a part of the drain electrode 311 is formed in the thirdinsulating layer 313. A pixel electrode 312 connected to the drainelectrode 311 is formed in the contact hole. By the above-mentionedmethod, a polysilicon display device in accordance with an embodiment ofthe present invention can be formed without injecting impurity ions toform source and drain electrodes or having to perform seperateactivation process.

Next, with reference to FIGS. 4A to 4G, a process for fabricating aliquid crystal display device in accordance with another embodiment ofthe present invention will be described. In particular, in the secondembodiment, a process of fabricating a polysilicon display device willbe described by a five-mask process using a diffraction exposure method.

As shown in FIG. 4A, a process for forming a gate electrode 403 on asubstrate 401 is performed. Before forming the gate electrode, a bufferlayer 402 which may be composed of silicon nitride or silicon oxide isformed on the substrate 401 in order to prevent impurity ions in thesubstrate from being diffused into a subsequently formed active layer.

Next, a conductive layer, which may be compose of metal, is formed onthe buffer layer 402, and the conductive layer is patterned to form agate electrode 403 and a gate line (not shown).

Next, a first insulating layer 404 composed of silicon oxide or siliconnitride is formed on the substrate on which the gate electrode 403 isformed. Subsequently, a first amorphous silicon layer 405 is formed onthe first insulating layer 404.

Next, a photoresist is applied on the first amorphous silicon layer 405and patterned to form a photoresist pattern 406 on a channel region byusing a mask.

Next, a second amorphous silicon layer 407 is formed on the photoresistpattern 406 and the first amorphous silicon layer 405 by PECVD. At thistime, the second amorphous silicon layer 407 includes high densityimpurity ions. A mixture of the second amorphous silicon and the highdensity impurity ions may be formed by infusing the high densityimpurity ions into the chamber while the second amorphous silicon layer407 is deposited by PECVD. When a P-type TFT is formed, ions of theperiodic Group III, such as Boron, may be used as the impurity ions andin the case of a N-type TFT, ions of the Group V such as Phosphorous maybe used.

The second amorphous silicon layer 407 formed by the above methodinherently becomes an amorphous silicon layer in which the impurity ionsare intermixed. At this time, the second amorphous silicon layer 407does not have to be thick and may be formed with a predeterminedthickness capable of improving ohmic contact characteristics with ametal layer. In this embodiment, the first amorphous silicon layer 405can have a thickness of about 500 angstroms Å and the second amorphoussilicon layer 407 can have a thickness of about 200 angstroms Å.

Next, the photoresist pattern 406 and a portion of the second amorphoussilicon layer 407 formed on the photoresist pattern are removed at thesame time by a lift-off process. The lift-off process is the same asdescribed in the above-mentioned embodiment. By using this lift-offprocess, only the first amorphous silicon layer 405 is left on thechannel region, and other regions have a lamination structure of boththe first and second amorphous silicon layers 405 and 407.

Next, as shown in FIG. 4C, a process of crystallizing the formed firstand second amorphous silicon layers is performed. The crystallizationprocess comprises a step of performing dehydrogenation by heating theamorphous silicon layers 405 and 406 and a step of crystallizing theamorphous silicon layers. Since the crystallization process is the sameas described in the above-mentioned embodiment, this description isomitted in the present embodiment. After completing crystallization ofthe first and second amorphous silicon layers 405 and 407, a conductivelayer 408 is formed on the crystallized silicon layers and a photoresistis coated on the conductive layer 408. The photoresist is exposed by aslit mask to thereby form a stepped photoresist pattern 409 having athinner thickness at an upper portion of the channel region than atother regions.

Next, as shown in FIG. 4E, the conductive layer 408, the first siliconlayer 405, the second silicon layer 407 and the first insulating layer404 are removed by an etching process using the slit-exposed photoresistpattern 409 as a mask so as to define an active layer. After patterningthe active layer, the photoresist pattern 409 is ashed. As a result ofthe ashing, the thinner portion of the photoresist pattern 409 on theupper portion of the channel region is removed so that the conductivelayer 408 on the channel region is exposed.

When the conductive layer 408 on the channel is exposed, the conductivelayer is then etched to expose the active layer 405 a under theconductive layer in the channel region. As a result, as shown in FIG.4F, the conductive layer 408 on the active layer 405 a is separated intosource and drain electrodes 410 and 411.

Next, the ashed photoresist pattern remaining on the source and drainelectrodes 410 an 411 is stripped and a second insulating layer 412,passivation layer, is formed on the source and drain electrodes. Thesecond insulating layer may be an inorganic layer having the samematerials as the above-mentioned embodiment.

After forming the second insulating layer 412, as shown in FIG. 4F, acontact hole 413 exposing the drain electrode 411 is formed in thesecond insulating layer.

After forming the contact hole 413, as shown in FIG. 4G, a pixelelectrode 414 is formed on the second insulating layer 412. As a result,a thin film transistor may be formed through a five-mask process byusing a first mask for forming a gate electrode, a second mask forforming a photoresist pattern, a third mask as a slit mask for formingsource and drain electrodes, a fourth mask for forming a contact hole onthe drain electrode and a fifth mask for forming a pixel electrode.

As so far described, in the present invention, by forming a photoresistpattern on a channel region, forming an amorphous silicon layer on thephotoresist pattern in an atmosphere of containing impurity ions,removing the photoresist and the amorphous silicon layer by a lift-offmethod, and automatically activating the amorphous silicon layer duringthe crystallization process, a separate ion-injection process does nothave to be performed to form drain and source regions. In addition,since there is no need for separately performing a process of activatingthe amorphous silicon layer into which ions are injected, ion-injectionequipment and equipment for activating the silicon layer into which ionsare injected and the steps may decrease. Accordingly, the number ofprocesses can be reduced.

Since source and drain regions of a liquid crystal display device of thepresent invention are not formed by an ion injection method, thecrystalline lattice of the polysilicon is not damaged. In addition, aprocess dedicated solely to activation is not performed. Further, sourceand drain regions composed of the polysilicon layers are of good qualityand have improved contact characteristics.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A method for fabricating a polysilicon liquid crystal display device,comprising: forming a first amorphous silicon layer on a substrate;forming a photoresist pattern on the first amorphous silicon layer;forming a second amorphous silicon layer over the photoresist patternand the first amorphous silicon layer; defining a channel region on thefirst amorphous silicon layer; crystallizing the first and secondsilicon layers; forming an active layer by patterning the crystallizedsilicon layers; forming a first insulating layer on the active layer;forming a gate electrode on the first insulating layer; forming sourceand drain electrodes electrically connected to the active layer; andforming a pixel electrode electrically connected to the drain electrode.2. The method of claim 1, wherein the forming the second amorphoussilicon layer includes: adding high density impurity ions to a plasmafor depositing the amorphous silicon.
 3. The method of claim 2, whereinthe high density impurity ions includes Group III or Group V type ions.4. The method of claim 1, wherein the defining the channel region on thefirst amorphous silicon layer is performed by lifting off thephotoresist pattern and a portion of the second amorphous silicon layeron the photoresist pattern.
 5. The method of claim 2, wherein theimpurity ions added in the second amorphous silicon layer are activatedwhile crystallizing the first and second amorphous silicon layers. 6.The method of claim 2, wherein the adding high density impurity ions tothe amorphous silicon includes: introducing the high density impurityions into a process chamber while the amorphous silicon is deposited. 7.A method of fabricating a polysilicon liquid crystal display device,comprising: forming a gate electrode on a substrate; forming a firstinsulating layer on the gate electrode; forming a first amorphoussilicon layer on the first insulating layer; forming a photoresistpattern on the first amorphous silicon layer; forming a second amorphoussilicon layer over the photoresist pattern and the first amorphoussilicon layer; defining a channel region on the first amorphous siliconlayer; crystallizing the first and second amorphous silicon layers;defining an active layer; forming source and drain electrodes on thecrystallized second silicon layers; and forming a pixel electrodeelectrically connected to the drain electrode.
 8. The method of claim 7,wherein the forming the second amorphous silicon layer includes: addinghigh density impurity ions to a plasma for depositing the amorphoussilicon.
 9. The method of claim 8, wherein the high density impurityions includes Group III or Group V type ions.
 10. The method of claim 7,wherein defining the channel region on the first amorphous silicon layeris performed by lift-off the photoresist pattern and a portion of thesecond amorphous silicon layer on the photoresist pattern.
 11. A methodfor fabricating a liquid crystal display device, comprising: forming afirst amorphous silicon layer on a substrate; forming an organic layerpattern on the first amorphous silicon layer; forming a second amorphoussilicon having high density impurity ions on the organic layer pattern;and removing the organic layer pattern and a portion of the secondamorphous silicon layer on the organic layer at the same time.
 12. Themethod of claim 11, wherein removing the organic layer pattern and thesecond amorphous silicon layer on the organic layer pattern at the sametime is performed by a lift-off process.
 13. The method of claim 11,wherein the organic layer pattern includes a photoresist organic layer.14. The method of claim 11, further comprising: crystallizing the firstamorphous silicon layer and remaining second amorphous silicon layer.15. The method of claim 11, wherein a channel region is defined byremoving the organic layer pattern and a portion of the second amorphoussilicon layer on the organic layer at the same time.
 16. The method ofclaim 14, wherein the first and second amorphous silicon layers areactivated during crystallization.